Friction modifier compounds used in lubricant formulations may generally have a formula comprising a polar functional group attached to a hydrophobic hydrocarbon chain that preferably has a suitable formula and a suitable number of carbon atoms in order to exhibit oil solubility. Molecules of this nature may typically be used in amounts ranging from about 0.01 to about 0.5 wt. %, based on the weight of the fully formulated lubricant, and may be capable of providing a suitable degree of fresh oil shudder protection in automatic transmission fluids (ATFs) or other lubricating fluids; however, they may fail in durability testing due to a limited quantity present in the oil. One approach to circumvent this problem is to use friction modifiers at levels ranging as high as from about 3 to about 5 wt. %. However, an important limitation to this practice may involve the low temperature viscometrics property, which is measured as Brookfield Viscosity at −40° C. (BV −40). Finished lubricants having a high level of conventional friction modifiers may suffer from unacceptably high BV −40 values.
Typifying the aforementioned friction modifier compounds are additives for lubricants as described in EP 0020037A1 that may be characterized as oil-soluble aliphatic hydrocarbyl-substituted succinimide or succinamide materials wherein the hydrocarbyl group that is bonded to the succinimide group contains 12 to 36 carbon atoms and is preferably derived from a linear α-olefin, and more preferably derived from an isomerized linear α-olefin, in order to improve oil solubility.
A friction modifier according to EP 0020037A1, with the hydrocarbyl group based on an isomerized linear α-olefin, suffers from poor low temperature viscometrics, when measured as Brookfield Viscosity at −40° C. (BV −40). For instance, a formulation representative of a preferred lubricant additive in EP 0020037A1 may be formulated as a friction modifier in a power transmitting fluid formulation that may have adequate durability performance. However, a formulation containing such a friction modifier at higher concentrations, such as 3.5% by weight, suffers from grossly inadequate low temperature viscometrics. At low temperature the viscosity of such a formulation may be as high as about 30,000 cP, which is a commercially undesirable viscosity with respect to automatic transmission lubricants.
In principle, the poor low temperature viscometrics might be compensated for by adding an expensive synthetic ester to the lubricant. However, the amount of synthetic ester required in order to lower the BV −40 to the desired level of roughly 10,000 cP or less is simply not economically attractive due to the increase in overall production costs.
Yet another drawback to the conventional friction modifier formulation relates to its aesthetic features apparent in the form of slight haze or sediment at higher treat rates, such as about 3.5 wt. %. Due to its dark brown color, finished oils with this formulation at high treat rates are darker in color. A still further drawback is that this formulation is solid at room temperature and requires additional heating for transfer and blending.
There is no apparent disclosure or recognition in EP 0020037A1 suggesting an awareness of the low temperature performance problem with its preferred friction modifiers, nor is there any suggestion of a commercially viable solution to the low temperature viscometrics problem.
Accordingly, there is a need for an economically attractive friction modifier that may be used at higher concentration levels, such as greater than 2% by weight of the fully formulated fluid, in a lubricating fluid or power transmitting fluid, such as an automatic transmission fluid (ATF), to provide improved friction durability. Such a friction modifier may also provide an aesthetically acceptable product that does not suffer from the poor low temperature properties that are observed with conventional formulations incorporating preferred friction modifiers according to EP 0020037A1.
It has now been discovered that certain novel compounds as described hereinbelow may be readily formulated into lubricating compositions to afford a unique solution for providing desired characteristics, such as improved friction durability and low temperature viscometric properties.